Programmable power supply



July 10, 1962 R. C. AKERS Filed April 10, 1958 2 Sheets-Sheet 1 lo M IPOWER SERIES 0x120 1; SOURCE REGULATOR 7 E RESISTOR l 3! l3 0/ 2DIFFERENCE AMPLIFIER VOLTAGE |5 REFERENCE PROGRAMMING SIGNALS KNVENTOR.

ROBERT C. AKERS AGENT July 10, 1962 R. c. AKERS PROGRAMMABLE POWERSUPPLY 2 Sheets-Sheet 2 Filed April 10, 1958 "2 SERIES REGULATOR IIRESISTOR POWER SOURCE l0 DIFFERENCE AMPLIFIER VOLTAGE REFERENCE l5PROGRAMMABLE RESISTOR NETWORK IS PROGRAMMING SIGNALS EIG.2

INVENTOR.

ROBERT c. AKERS BY 651 2 AGENT United States Patent Office 3,044,007Patented July 10, 1962 3,044,007 PROGRAMMABLE POWER SUPPLY Robert C.Akers, Long Beach, Calif., assignor to North American Aviation, Inc.

Filed Apr. 10, 1958, Ser. No. 727,703 6 Claims. (Cl. 32322) Thisinvention relates to power supplies, and more particularly to powersupplies having an output voltage programmed in response to a binarycoded signal input.

Although the present invention has general application, it isparticularly adapted for use in an automatic checkout system. In thistype of system a sequence of tests are programmed in a memory storageelement. Magnetic or punched paper tape are commonly utilized for thispurpose. Often times, the testing of a circuit, component, or systemrequires that the circuit etc. be tested while energized by one or moreprecision voltage The magnitudes of voltages required will often varyfor different stages of a single test, and of course, for variouscomponents. The present invention provides a programmable power supplyhaving an output voltage under the control of a binary coded signal. Therequired testing analog voltages may thus be obtained in accordance withdigital binary signals recorded in the memory storage element.

Accordingly, it is an object of this invention to provide an improvedprogrammable power supply.

It is another object of this invention to provide a power supply whoseoutput voltage is under the control of a binary coded signal.

It is still another object of this invention to provide a programmablepower supply adapted for a plurality of binary coding arrangements.

A further object of this invention is to provide an improveddigitalto-analog converter.

Other and further objects, features and advantages of the invention willbecome apparent as the description proceeds.

The present invention accomplishes the above cite-d objects by providinga power supply whose output varies linearly with a change in resistancein the voltage regulation circuitry. A resistor network programmableaccording to a predetermined number system is utilized to vary thisresistance thereby controlling the power supply output voltage inresponse to digital input signals.

A more thorough understanding of the invention may be obtained by astudy of the following detailed description taken in connection with theaccompanying drawings in which:

FIG. 1 illustrates a programmable power supply constructed in accordancewith this invention; and

FIG. 2 illustrates schematically the programmable power supply shown inFIG. 1.

Referring now to FIG. 1, a power source 10 is connected to drive outputterminals 12a and 12b. Series regulator 11 is connected between anoutput of power source 10 and output terminal 12a. The voltage potentialbetween the input and output of series regulator 11 varies with a changein the signal on line 31. The voltage between the output terminals 120and 12b is dependent upon the voltages at the terminals of power source10 and across the series regulator 11. Therefore, assuming that theoutput voltage of power source 10 is a constant, the voltage between theoutput terminals 12:: and 12b will vary as the signal on line 31 varies.

Feedback resistor 13, connected to the output of series regulator 11, isutilized to efiect a feedback signal according to the voltage acrosssaid output terminals thereby achieving voltage regulation. As shown,resistor 13 and programmableresistor network 16 are connected in seriesacross the potential existing between the output terminals 12a and 12!).One input to difference amplifier 14 appears on line 32 as the voltagedrop across resistor 13. Another input to ditlerence amplifier 14appears on line 34 as the fixed potential output of voltage reference15. Diiference amplifier 14 may be any circuitry which has for itsoutput the difference between the voltages appearing on lines 34 and 32.Therefore, the input to amplifier 30 is the difference between theoutput of voltage reference 15 and the voltage across resistor 13. Afeedback loop is completed by connect ing the output of amplifier 30 toseries regulator 11 by line 31 to effect control of the voltage dropacross the regulator and thus control the output at terminals 12a, 12b.

The circuitry heretofore described operates to achieve voltageregulation as follows: Current l shown in FIG. 1 is caused to flowthrough series connected feedback resistor 13 and programmable resistornetwork 16 whenever a voltage potential exists between output terminal12a and 12b. The voltage potential on line 32 is the voltage drop acrossresistor 13 due to the fiow of current I The potential existing on line34 is a constant determined by voltage referencelS. Whenever thepotentials on line 32 and 34 are unequal, an error signal supplied bydifference amplifier 14 will be amplified in amplifier 30 and willeffect a change in the voltage drop across series regulator 11. Thevoltage at the output terminals 12a and 12b will thus be driven to avalue such that the current 1 flowing through resistor 13 will cause avoltage drop across resistor 13 equal in magnitude to the voltage outputof voltage reference 15. The value of current I; will remain at thevalue determined by voltage reference 15 and resistor 13 until such timeas there is a variation in the voltage between output terminals 12a and12b. For example, a change in potential between these terminals would becaused by a change in the voltage of power source 10. Any change inoutput potential will cause a variation in the flow of current I so asto reflect a different potential at junction 33. Since the potential online 32 is no longer the same as the potential on line 34, thedifference amplifier will respond so as to supply an error signal outputwhich drives amplifier 30. The amplifier error signal in line 31 affectsthe potential across series regulator 11 in such a way as to produce achange in voltage drop across regulator 11 that opposes the change inoutput voltage.

Difference amplifier 14 and the circuitry associated therewith alsoprovide a means of selecting a range of output potentials. As notedabove, the potential between terminals 12a and 12b will tend to remainat a predetermined value so as to equate the voltage drop acrossresistor 13 with that of voltage reference 15. If, however, theresistance of programmable resistor network 16 is changed, the value ofcurrent I will also tend to change in an inverse manner. As in the caseof voltage regulation, a change in the value of current I1 willimmediately cause a change in the voltage across resistor 13 therebyunbalancing the inputs to difference amplifier 14. Series regulator 11produces a change in voltage at terminals 12a-12b so as to drive thecurrent I to its original value, thereby equating the voltages on lines32 and 34. Thus, the voltage at the output terminals 12a-12b may becontrolled by varying the resistance of programmable resistor network.16. By suitably selecting the cicuit parameters, and in particularselecting an amplifier 30 having a high gain, the output voltage may bemade to vary linearly with a change in resistance of programmableresistornetwork 16. i

Programmable resistor network 16 includes a plurality of seriesconnected resistors 17, 18, 19, 20, 21, 22, 23, 24

and 25. "Relays 41 4'1, 42, 43, 44, 4'5, 46, 47 and 48 have respectivecontact pairs 60, 61, 62, 63, 64, 65, 66, 67 and 68. Each of thesecontact pairs are connected to opposite sides of a different one of theresistors 17 through 25. Terminal 80 is connected to a connecting linecommon to all of the relays 40 to 48. Terminals 81, 82, 83, 84, 85, 86,87, 88 and 89 are each respectively connected to one of the relays 40 to48. Thus, if a programming signal is applied between terminal 88 and anyone of the terminals 81 through 89, the respective relay will beactuated thereby efiecting an operation of the associated contact. Thecontacts 69 through 68 are normally closed contacts as illustrated inFIG. 1. The associated resistors are thereby shunted whenever aprogramming signal is absent. Therefore, if no pragramrning signals arepresent, the resistance of programmable resistor network 16 is zero ohm.Contrariwise, if a programming signal is pre ent between terminal 80 andeach of the terminals 81 through 89, the resistance of programmableresistance network 16 is a mixamum resistance equal to the sum of eachof the individual resistors 17 through 25.

Resistors 17 through 25 are assigned values according to a predeterminednumber system. An example of one such system is an ordinary binary code(tabulated in Table 1). The values assigned to resistors 17 through 25are those which would be utilized in a power supply whose output voltageis equal to one volt per thousand ohm change in resistance of theprogrammable resistor network 16. So long as the power supply output islinear with a change in resistance in the programmable resistor network16, the actual ratio of resistance change to output voltage change isimmaterial and the values of resistances 17 through 25 would be changedaccordingly, i.e., if the output voltage were equal to one volt perhundred ohm change, the value of each of the resistors 17 through 25Would be divided by 10.

Table 2 illustrates the programming signals required for output voltagesin the range of zero to ten volts for an ordinary binary code. In this,and subsequent tables, a zero indicates the absence of a programmingsignal and a 1 indicates the presence of a programming signal. The tablecould, of course, be enlarged in a similar manner so as to produce anydecimal voltage between zero and 511 volts depending upon theprogramming signals applied to terminals 81 through 89.

Table 2 Programming Signalsrdinery Binary Decimal Voltage, volts 0 0 0 00 0 0 0 0 0 0 0 0 0 0 O 0 1 0 0 0 0 0 0 0 1 O 0 0 0 O 0 0 0 1 1 O 0 0 0O O 1 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 1 1 1 0 0 0 00 1 0 0 0 0 0 0 0 0 1 O 0 1. 0 0 0 0 0 1 0 1 0 Often times it isdesirable that each decimal digit be coded in binary. There are manyways of coding the decimal digits, i.e., of combining several binarydigits to represent one decimal digit. All of the binary coded decimalsystems require at least four bits, and involve assigning some value toeach. Two systems in common use are the 8-4-2-1 and the 242-1 systems.The 8-4-21 system assigns the same weights to the bits as in ordinarybinary notation shown in Tables 1 and 2. The values of resistances 17 to25 coded for this system are recorded in Table 3. Table 4 tabulates theprogramming signals required for producing the decimal voltages fromzero to ten volts. Table 4 could be enlarged in like manner to include arange of 0 to 199 volts.

Table 3 BINARY CODED DECIMAL (8-4-2-1) Value, Output Resistor No. ohmsVoltage,

volts 1K 1 2K 2 4K 4- 8K 8 10K 10 20K 20 40K 40 80K 80 100K 100 Table 4Programming Signals-(BOD, 8-4-2-1) Decimal Voltage, volts 0 0 0 0 O 0 O0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 O 0 0 0 0 1 1 0 0 0 0 0 0 10 0 0 0 0 0 0 0 1 0 1 0 (l 0 0 0 0 1 1 0 O 0 0 0 0 0 1 1 1 0 0 0 0 0 1 O0 0 0 0 0 0 0 1 0 O 1 O 0 0 0 1 0 0 0 O The 2-42-1 or modified binarycoded decimal system has several features which may be desirable indigitally controlled equipment. This system has the following twocharacteristics: (1) The nines complement of a decimal digit can beformed by complementing each binary digit. (2) When any two binary codeddigits are added in binary, the sum always contains five binary digitsif it is ten or greater and four binary digits if it is less than ten.The value to be assigned the resistors in the programmable resistivenetwork 16 are tabulated in Table 5 for this system. Table 6 illustratesthe programming signals required for obtaining the decimal voltages fromzero to ten volts. Table 6 could be enlarged in like manner to include a60 range of 9 to 199 volts.

Value,

Output ohms Voltage, volts Resistor Table 6 Programming Signals (BOD,2-4-2-1) Decimal Voltage, volts 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 00 0 0 0 0 1 0 0 0 O 0 0 0 0 1 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 1 1 0 00 0 0 1 l 0 0 0 0 0 0 0 1 1 0 1 0 0 0 0 O 1 1 1 0 0 0 0 0 0 1 1 1 1 0 00 0 1 0 0 0 0 The two characteristics of the 2-4-24 system mentionedabove may be checked by referring to Table 6. Thus, the nines complementof five is four; the representations are respectively 1011 and 0100,which are seen to have binary zeros and ones reversed. Also, adding fiveand four in decimal causes no carry; adding 1011 and 0100 does not.Adding five and five does; adding 1011 and 1011 does.

The programming signals applied to terminals 80 through 89 may beconveniently recorded on any one of many memory elements. 'For example,punched paper tape or paper cards or magnetic tape or drums are alladaptable for storing the digital programming signals. The coding systemselected may be one of those described above or some other binary schemeknown in the art. In effect, the programmable power supply describedabove effects a digital-to-analog conversion. The digital information isapplied as programming signals and the output of the power supply is adirect representation of the physical quantity desired (rather thanrepresentations of intermediate symbols applied as programming signals),i.e., an analog output.

FIG. 2 illustrates schematically, circuitry which may be utilized toconstruct the programmable power supply shown in FIG. 1. Power sourcecomprises a direct current source of conventional design. Alternatingcurrent source 100 energizes a full wave rectification circuit includingcenter tapped transformer 101 and diodes 102 and 103. The output of thisfull wave circuit is connected to filter 104 which produces a reducedripple factor. The output of filter 104 is coupled to the plate oftetrode 106 via resistor 105; The screen grid of this tube is biased byconnecting it to the plate via resistor 112. The cathode of tetrode 106is connected directly to output terminal 12a. Output terminal 12b isconnected directly to the output of filter 104.

Feedback resistor 13 comprises series connected resistor 107 andvariable resistor 108. Resistor 13 is connected between junction 33 andterminal 12a. Diiference amplifier 14 includes a dual triode 109 havinggn'ds 110 and 111. Grid 111 is connected to junction 33 via connectingline 32. Grid 110 is connected to the output of voltage reference 15.The cathodes of dual triode 109 are connected together and to thenegative side of battery 120 through biasing and coupling resistor 121.Plate 123 is connected directly to ground while plate 122 is connectedto ground through resistor 124. The plate voltage supply for the dualtriode 109 is completed by connecting the positive terminal of battery120 to ground as illustrated.

The output of difierence amplifier 14 is taken from the plate 122 whichis connected directly to the input of amplifier 30. Amplifier 30 is acircuit of suflicient gain so as to make the output volt-ag betweenterminals 12a and 12b vary linearly with a change in resistance ofprogrammable resistor network 16.

Voltage reference includes a constant voltage tube 125 in series with avariable resistor 126. In parallel with these .two components isresistor 127. A cold-cathode gaseous discharge tube known in the art asa glow tube is commonly used as constant voltage tube 125. This tube ischaracterized by having a constant voltage between its terminals over aconsiderable range of current flow through the tube. In order to supplythe breakdown voltage for the tube, constant voltage tube 125 isconnected between a midpoint of battery and the negative terminalthereof. Resistor 128 is connected between the cathode of tube and thenegative terminal of battery 120.

The circuitry of programmable resistor network 16 is shown in blockdiagram form in FIG. 2 since it was shown in detail in FIG. 1. In thecircuit shown in FIG. 2 it has'been found convenient to include a secondconstant voltage tube 130 in series between programmable resistornetwork 16 and output terminal 12b. Direct current power supply 131 isconnected across the constant voltage tube 130 through resistor 132 tosupply the breakdown voltage for the tube. It has further been foundconvenient to operate the terminal 12a at a voltage below ground. Outputterminal 12a is therefore connected to the midpoint of battery 120.This, of course, does not affect the output voltages of the power supplysince they are measured between terminals 12a and 12b.

The addition of constant voltage tube '130 in the circuit permits thecurrent I to flow at its predetermined value when zero voltage isrequired between the output terminals 12a and 12b. Were this voltagesource not included, any current flow through resistor 13 would producea voltage drop seen between output terminals 12a and 12b. With theconstant voltage tube 130 in circuit, the voltage drop across this tubeexactly balances the voltage drop across resistor 13 in the zero voltageoutput condition, thereby permitting the predetermined current flowthrough the resistor 13 at this time.

In the operation of the circuit shown in FIG. 2, programming signals areapplied so as to obtain a zero voltage output across terminals 12a and12b. Normally, in this condition none of the relays 40 through 48 areactuated (FIG. 1). The resistance of programmable resistor network 16 inthis condition is, of course, zero ohms. Variable resistor 126 in thevoltage reference 15 is now changed so as to obtain zero voltage betweenterminals 12a and 12b. This adjustment provides a convenient means forcorrecting any unbalance between the triodes of dual triode 109. Afurther adjustment is provided by variable resistor 108 in the maximumvoltage output condition. In this condition programming signals areacquired so as to normally operate all of the relays 40 through 48thereby maximizing the resistive impedance of network 16 (FIG. 1). Theresistance of variable resistor 108 is now changed so as to obtain the,predetermined voltage at the output terminals 12a and 12b. With theseadjustments having been made, the programmable power supply will deliverany voltage between zero and the maximum depending upon the digitalsignals applied to the programmable resistor network.

Although the invention has been described and illustrated in detail, itis to be clearly understood that the same is by way of illustration andexample only and is not to be taken by way of limitation, the spirit andscope of this invention being limited only by the terms of the appendedclaims.

I claim:

1. In combination, a source of direct voltage having first and secondoutput terminals; a third output terminal; a series regulator connectedbetween said first and third output terminals and having an inputelectrode for controlling the impedance of said regulator; a differenceamplifier having an output terminal coupled with said regulator inputterminal, a commonterminal connected to said third output terminal, anda pair of input terminals; a voltage reference connected between saidthird output terminal and one of said diiference amplifier inputterminals, a feedback resistor connected between the other of saiddifference amplifier input terminals and said third output terminal; anda resistor network programmable in response to digital input signalsconnected between said other difference amplifier input terminal andsaid second output terminal.

2. The combination defined in claim 1 wherein said programmable resistornetwork includes a plurality of series connected resistons, the valuesof which are assigned according to a binary number system, and aplurality of relays each respectively having a normally closed contactpair in shunt connection with a different one of said series connectedresistors, said relays being adapted for energization by said digitalinput signals.

3. The combination defined in claim 1 wherein said feeedback resistorincludes a fixed and variable resistance connected in series therebyproviding a means for precisely adjusting the predetermined maximumvoltage obtainable between said first and second output terminals.

4. The combination defined in claim 1 wherein a second voltage referenceis connected in series between said resistor network and said secondoutput terminal.

5. The combination defined in claim 1 wherein said voltage referenceincludes a series circuit having a coldcathode gaseous discharge tube inseries with a variable resistance, and a resistance in parallel withsaid series circuit, said variable resistance providing a means forprecisely adjusting the voltage between said first and second outputterminals for zero voltage with no digital input signals applied to saidprogrammable power supply.

6. In combination, a source of direct voltage having first and secondterminals; a third output terminal; a regulating device including avacuum tube having a plate, a cathode, and a grid; said plate beingconnected to said first output terminal, said cathode being connected tosaid third output terminal; a difierence amplifier comprising a pair ofvacuum tubes each having a plate, a cathode, and a grid; the cathodes ofsaid difierence amplifier being connected together and to a commonterminal; said common terminal being connected to said third outputterminal; a first voltage reference connected between said third outputterminal and the grid of one of said difference amplifier tubes; afeedback resistor connected between the grid of the other of saiddifference amplifier tubes and said third output terminal; a seriescircuit including a group of digitally weighted series connectedresistors and a second voltage reference connected between the grid ofsaid other difference amplifier tube and said second output terminal; agroup of relay each individual to a different one of the resistors ofsaid group and each having a contact pair respectively connected toopposite sides of its associated resistor; a group of control terminalpairs, each pair of control terminals being uniquely connected to one ofsaid relays; and an amplifier connected between the plate of one of saiddifference amplifier tubes and the cathode of said regulating devicetube.

References Cited in the file of this patent UNITED STATES PATENTS2,468,850 Trucksess May 3, 1949 2,474,269 Martinez June 28, 19492,573,405 Clark Oct. 30, 1951 2,762,038 Lubkin Sept. 4, 1956 2,784,369Fenemore Mar. 5, 1957 2,808,560 Jaffe Oct. 1, 1957 2,841,758 Wright etal. July 1, 1958 2,892,147 Bell June 23, 1959

